1. Field of the Disclosure
This invention relates to articles with non-stick fluoropolymer finishes exhibiting improved scratch resistance.
2. Description of the Related Art
The technology of forming a non-stick fluoropolymer finish on a substrate, such as aluminum, to form a release surface for such applications as cookware has typically involved the use of at least two coats on the substrate, an undercoat typically called a primer to adhere to the substrate, and an overcoat to provide the non-stick coating (finish).
It has become known to incorporate relatively large particles of inorganic, non-metallic particles into the primer layer to increase abrasion resistance of the non-stick finish. European Patent No. 0 724 915 to Bignami discloses the use of cristobilite, which is a SiO2 mineral having a Moh's hardness of 6.5 (corresponds to a Knoop hardness of 820), in the primer layer. U.S. Pat. No. 6,291,054 to Thomas et al. and U.S. Pat. No. 6,761,964 to Tannenbaum disclose the use of large ceramic particles, preferably having a Knoop hardness of at least 1200, in the primer layer.
In addition to abrasion resistance, it is desirable to improve the scratch resistance of non-stick finishes. In U.S. Patent Application No. 2004/0261932 to Buffard et al, small ceramic particles of less that 4 μm diameter with a “quasi-spherical” shape are used in the primer of a non-stick finish in an attempt to improve both scratch and abrasion resistance.
Others have suggested including other types of particles, such as whiskers to improve the performance of non-stick finishes. For example, whisker materials have been used in primers of non-stick coating systems to improve the adhesion of subsequent topcoats. U.S. Pat. No. 5,560,978 to Leech describes a two-coat system with a basecoat (i.e., primer) that includes a high temperature binder resin and a filamentary powder, e.g., a nickel filamentary powder, to form a spongelike material with a rough surface and an internal structure containing interlocking channels. The advantage of creating this spongelike material with a roughened surface is that it enables a fluoropolymer topcoat to be anchored therein, and thus improves adhesion of the topcoat to the basecoat.
Alternatively, whisker materials have been used in topcoats of non-stick finishes to improve wear resistance. In Japanese Patent No. 3471562(B2) to Maeda et al., potassium hexatitanate whiskers are used in the fluoropolymer topcoat of one-coat and two-coat systems to improve the wear and scratch resistance of the non-stick surface. The coatings of Maeda further include spherical ceramic pigments (i.e., glass beads containing SiO2 and Al2O3) to improve abrasion resistance.